The predatory functional response is one of the important components of the interaction between predator and prey populations. This response has not been measured for fish predators and fish prey, in spite of the demonstrated importance of predation in regulating numbers in populations such as the juvenile salmon system used in this thesis. Laboratory exeriments were conducted to determine the form of the functional response of the prickly sculpin (Cottus asper), a common freshwater predator, to density of sockeye salmon fry, Oncorhynchus nerka. An alternative prey, chum salmon eggs (Oncorhynchus keta), were presented to the predator with the salmon fry, in order to facilitate switching at low fry densities and possibly lead to a sigmoid (type III) response. Initial experiments showed that sculpin feeding rate did not substantially differ from day to night; that in the absence of food, hunger increased to a maximum after about seven days' starvation; and that a density of 400 chum salmon eggs in a 2000 1 tank produced maximum consumption level by sculpins of 160 mm total length. The functional response experiments did not indicate a sigmoid rise in consumption over low fry densities. However, the initial decelerated rise in consumption was followed by an anomalous drop in response and a subsequent rise in response. It is suggested that this may result from the summation of separate responses through different sensory modalities, or from interference with predation by fry at intermediate densities. This shape of functional response may imply a stable local equilibrium at intermediate densities of salmon. Sculpins probably have a significant impact on fry numbers only at very localized points in space and time, such as at the outlets of tidal creeks on a falling tide. / Science, Faculty of / Zoology, Department of / Graduate

The history, management and ecology of the European red mite, Panonvchus ulmi Koch, and two important phytoseiid predators, Typhiodromus caudiglans Schuster and Typhiodromus occidentalis Nesbitt were reviewed. The roles and interactions of dispersal, predation and weather in the orchard mite system were examined. Field experiments in an apple orchard with well-established phytoseiid and European red mite (ERM) populations showed that Typhiodromus rarely move among or between trees and the ground cover, either by air or via the trunk. They were incapable, within a single season, of repopulating trees from which phytoseiids had been removed by early-season carbaryl application, even though these trees supported high prey populations and were interspersed among unsprayed trees well-populated with Typhiodromus and the ERM. Large numbers of sticky traps captured very few aerially dispersing phytoseiids. In contrast, their ERM prey actively dispersed within trees and throughout the orchard. Mite densities were uncorrelated with leaf chlorophyll content; within-tree dispersal was not directly determined by leaf condition. Adult females were greatly over-represented in aerially-dispersing ERM emigrants in comparison with populations on the apple trees. No density threshold effect on ERM dispersal was discernible on a per-tree basis. Aerial dispersal was extensive and appeared to depend on the weather more mites disperse on warm and calm days than on cool or windy days. ERM dispersal via the tree trunk was minimal and the presence of weeds resulted in only a slight increase in ERM density on the trees. The phytoseiids affected the ERM by reducing population densities, by reducing the proportion of immatures, and by decreasing the degree of prey aggregation (as represented by frequency distribution of leaf counts). The consequences of low predator dispersal and high prey dispersal in a weather-dependent system are discussed. Results of computer simulation of the development, predation, and dispersal are presented. Dispersal (immigration and emigration) allow the phytoseiid populations in the single-tree model to persist and control the ERM. In simulations of the interaction of Typhlodromus with the ERM, the interaction of dispersal and temperature-related processes is strong and non-linear, and may operate through several processes. / Land and Food Systems, Faculty of / Graduate

This study focuses on ways that the size distribution of individuals influences the types and intensities of competitive interactions within a population of aquatic arthropod predators. Three field experiments and one laboratory experiment were designed to test for feeding interference, interference mortality, and dispersal effects within and between larval size classes of the primarily semivoltine dragonfly Tetragoneuria cynosura in Bays Mountain Lake. One field experiment documented the temporal pattern of colonization of large-mesh cylinders by the small, first-year-class larvae during a 30-day period; the results are consistent with passive (density-independent) colonization. A second field experiment examined the effect of large, second-year-class larvae at densities of 1 or 3 per cylinder (14 or 42 m-2) on colonization by small larvae; this colonization was inhibited at the high density of large larvae. In the laboratory experiment, when larvae of the two size-classes were together in the same aquarium, small larvae moved around less than when by themselves (dispersal inhibition). Thus the inhibition of colonization observed in the field may result from interference mortality, rather than from a flight response to the presence of larger conspecifics. To evaluate this interpretation, the third field experiment measured the in-situ functional response of large larvae to each other and to their small conspecific prey. Results suggest a type 1 (linear) functional response, with feeding inteference among large larvae. Moreover, the interference mortality inflicted by larger larvae on smaller conspecifics was apparently more intense on larger individuals within the small size-class. Taken together, the three field experiments and a statistical power analysis show how colonization and interference interact to determine the local density of small larvae, and why such interference effects are difficult to detect experimentally in the field.

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Field experiments using small replicated enclosures focused on interactions between larval populations of Epitheca cynosura and Ladona deplanata (Odonata: Anisoptera) - two species that emerge in early spring. The presence of Epitheca reduced the total biomass of Ladona, but Ladona had no significant effect on Epitheca. These early-emerging species reduced the biomass of small instars of late-emerging Anisoptera which colonized enclosures during the experiments; and the late-emerging Anisoptera seem to have inhibited colonization by Zygoptera larvae. Results are consistent with the importance of predatory (cannibalism or mutual predation) interactions in this community.

Environmental factors can have large impacts in shaping the way that animals behave. Biotic elements, such as predators and conspecifics that individuals interact with, are two environmental factors that animals may encounter on a regular basis. Here, we present the results of two studies examining the relationship of these biotic factors to behavior and personality in the degu (Octodon degus), a social rodent species endemic to central Chile. We found that long-term experimental isolation from predators has not impacted behavior, as indicated by an open field test in this species. We also found that social groups in this species do not adhere to either conformity or social niche specialization expectations with regard to personality, as determined in open field tests. These results raise further questions as to the mechanisms that govern behavior, as well as how personality evolved and is maintained in natural populations.

Primates have important ecological roles as seed dispersers and seed predators in tropical forests. Orangutans are large-bodied frugivores that consume a high diversity of plant species, however, relatively little is known about their ecological roles. Ecological interactions are critical processes for ecosystem dynamics, structures, and functions. This dissertation investigated Bornean orangutans’ (Pongo pygmaeus wurmbii) ecological roles by studying orangutan patterns of frugivory, seed dispersal, and seed predation, dispersed seed spatial patterns, and seed fate outcomes. This research was conducted at the Cabang Panti Research Station in Gunung Palung National Park, Borneo, Indonesia. Chapter 2 analyzes orangutan seed dispersal behavior using the seed dispersal effectiveness framework to identify which fruits orangutans are most effectively dispersing. Orangutans predated seeds more frequently than they spat or swallowed seeds. Additionally, the fruits preferred most by orangutans were highly predated. Despite the prevalence of seed predation, orangutans also frequently dispersed seeds, 71.8% of fecal samples contained seeds with a mean of 28 seeds (>2mm) per fecal sample. Chapter 3 models orangutan seed dispersal distances to understand how far orangutans are dispersing seeds across the landscape and if seeds are dispersed across habitat types. This study found orangutans dispersed seeds, on average, 400-650m. There were occasional long distance seed dispersal events, and the maximum dispersal distance was 2.2km. Both male and female orangutans dispersed seeds long distances (>1km). Unflanged male orangutans dispersed seeds the longest mean distances of the age-sex classes with the farthest mean maximum distances at the 80-hour gut retention time. In Chapter 4, the fate of seeds dispersed by orangutans is investigated along with the variation underlying the fate of dispersed seeds. Camera traps and seed tracking studies revealed the orangutan primary seed shadow was heavily reshaped post-dispersal. By 6-months post dispersal, most orangutan dispersed seeds (86-87%) had been removed, mostly by seed predators, and almost all of the remaining seeds (11-14%) had died. This dissertation reveals orangutans are involved in important ecological interactions. Orangutans disperse and predate high quantities of seeds from many plant genera, and the loss of the orangutan would likely negatively affect their natural ecosystems. / 2026-10-31T00:00:00Z

Identifying factors influencing kill rates or predation risk is crucial to relate predator effects on prey populations. In multi-predator landscapes, some predators may also perceive predation risk which may not only influence their distributions but also their effects on prey populations across landscapes. In the Upper Peninsula of Michigan, USA white-tailed deer (Odocoileus virginianus) exist in a multi-predator landscape which includes black bears (Ursus americanus), bobcats (Lynx rufus), coyotes (Canis latrans), and gray wolves (C. lupus). The objectives of this research were to examine spatial relationships among predators and their prey by identifying: 1) competition between wolves and coyotes, 2) factors influencing kill rates of predators, and 3) predator-specific predation risk for white-tailed deer fawns. We quantified the degree of temporal, dietary, and spatial overlap of wolves and coyotes at the population level to estimate the potential for interference competition and identify the mechanisms for how these sympatric canids coexist. We observed significant overlap across resource attributes yet the mechanisms through which wolves and coyotes coexist appear to be driven largely by how coyotes exploit differences in resource availability in heterogenous landscapes. We examined how heterogeneity in landscapes, search rate, and prey availability influence the time between kills for black bears, bobcats, coyotes, and wolves. Spatial heterogeneity in prey availability appeared to be a unifying extrinsic factor mediating time-to-kill across predators, potentially a consequence of more frequent reassessments of patch quality, which can reduce kill rates. We used white-tailed deer fawn predation sites to identify predator-specific predation risk with consideration for active predator occurrence, adult female white-tailed deer occurrence, linear features which may influence prey vulnerability, and habitat characteristics including horizontal cover and deer forage availability. Predator occurrence alone was a poor metric for predation risk. We identified differing landscapes of risk among ambush and cursorial foraging strategies which were more important for defining spatial variation in predation risk than predator density. These findings suggest that in a multi-predator landscape some predators may benefit from greater landscape heterogeneity due to availability of niche space, even though resource heterogeneity reduced predator efficacy and habitat complexity reduced predation risk for prey.

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